I think you misunderstand the meaning of “first world problem”. It’s meant to be a snark towards people who already have plenty of food and money and everything else and think that their perceived game issues are worthy of equal attention as the plights of the poor. Like complaining that one of the headlights on my Ferrari is dimmer than the other. In that context, this is absolutely a “first world problem”, snarkiness intended and appropriate.
On topic, conventional wisdom says that you should never, EVER feed any maxed hero with the exception of 2 stars… I’ve made a few rare exceptions in the case of 3 stars when I had duplicates (honestly, how many Banes and Priscas does one person need?). Okay, even if you already have 30 five star heroes, it’s highly unlikely that every one of them is fully leveled and ascended. The XP you get from feeding it will never come remotely close to justifying the lost time and resources you spent working on it. If you don’t mind throwing all of that away, then knock yourself out, it’s your game and you can play it however you want. It just seems like a massive waste of resources to me. I wouldn’t do it, personally, but the fact that you’re even considering it means you must have tons of resources to spare, in which case you probably won’t even notice the loss. Too bad this game doesn’t allow interplayer trading, I’d be willing to go as high as 500k food and 1000 common herbs for that trash hero of yours.